Preface

Radio astronomy is a child of this century, and has developed from the
work of
two pioneers in the 1930s to a fully developed branch of astronomy
today. That
development has brought with it an ambiguity, for high-frequency
technology has prospered, and it is no longer clear where radio
astronomy stops
and infrared astronomy begins. We propose a simple distinction: radio
astronomy
is the study of the universe by observing electromagnetic radiation after it
has been coherently amplified. When bolometers detect the radiation, the
subject is infrared astronomy: the use of amplifiers that preserve the
oscillatory character of the radiation - the
phase information - is the mark of radio astronomy. As time passes, an
increasingly large part of infrared astronomy will be subsumed into the
radio astronomy domain, but there is a natural boundary, imposed by the
laws of
quantum mechanics. The shorter the wavelength, the noisier the amplifier,
and by the time one reaches visible light, all amplifiers must become
too noisy for use except for a few special cases. When a coherent
amplifier is the instrument of choice, the infrared
astronomers will not hesitate to use it; the further development
of photon-counting infrared area detectors will make the demarcation
line between the regimes even clearer.

The plan of the book is twofold: we hope that the scope and impact of radio
astronomy observations wit be shown in the astrophysical discussion, and
at the same time we intend to give a brief but comprehensive treatment
of the
elegant methods that have developed. The breadth of the subject matter
necessarily limits the length of the treatment for each subject; the
authors have tried, therefore, to provide recent, comprehensive
references to the extent that they are available. In addition to the
astronomy graduate student and those professionally committed to radio
astronomy, there is a wider audience for whom this book is intended: the
interested astronomers from outside the field who want to be informed of
the principal ideas current in radio astronomy, and may even be thinking
of carrying out radio observations that would
complement other work in progress. Even though we have defined the
boundary of
radio astronomy for the sake of convenience, everyone is aware that the
boundaries between disciplines have dwindled in importance. Radio
observations would have been a baffling puzzle if the optical
identifications of sources had not been made, and both
radio and X-ray astronomers have long been aware of their kinship, since
both study high-energy phenomena, though at the opposite ends of the
spectrum. The techniques vary, but the astronomer of the future should
have access to the entire electromagnetic spectrum.

R.E. Burke
F. Graham-Smith

Acknowledgements

We acknowledge the generosity of many colleagues who provided illustrations and
other material for this book. We thank Wendy Hunter and Anne Conklin for
help in the preparation of the manuscript, and Andre Fletcher for his
careful reading of the text.